The Application of Newton’s Third Law of Motion…in a car crash?

To every action there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions. (Wikipedia)

In a nutshell, for every action force, there is a reaction force with equal magnitude in the opposite direction. Newton’s third law can be observed every day in anyone’s life, however, many of us don’t realize this. One example is when we are walking. Our legs push down on the ground, the opposite reaction making us walk forward. There are so many examples that display Newton’s Third Law of Motion that I could go on forever.

However, the scenario that I think best exemplifies Newton’s Third Law is a car crash.

Luckily there’s nobody inside!

How does the third law relate to a car crash?

In a car crash, the action force(s) are the cars colliding with each other. The reaction force is the force sent back due to the collision, which is what causes the damage to the car. When two cars are headed straight at each other, they are travelling in opposing directions. When they finally collide, if they apply the same amount of force, they will experience a reaction of equal magnitude. This causes the destruction of the front of both cars. Since FORCE IS EQUAL TO MASS MULTIPLIED BY ACCELERATION (F = ma), a car with a much greater mass will likely do better or even survive in a car crash compared to a car with a smaller mass, even if the two vehicles were travelling at the same acceleration.

Before being released to the market, new car models must be tested in a crash facility. There, they undergo and must pass safety tests, which involve the infamous crash test dummy in a car speeding head on at a barrier. Here is a video of a crash test:

This video shows that as the car is speeding up toward the wall, it’s acceleration increases, while mass stays constant. This causes the total force to increase. When the car makes contact with the barrier, there is reaction of equal magnitude that arises from the car making contact with the barrier. The reaction force is easily visible in a car crash, which is why it is such a great way to show how Newton’s Third Law can be applied to our lives.

In what other ways do you think Newton’s Third Law can be shown in our everyday lives? Leave it in the comment section :)

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15 Comment(s)

Shiv, Thanks for sharing that video; safety standards are so important to saving lives. Can you dig any deeper as to how they determine if a car is safe? How does the car absorb the force so that it’s not transferred to the passengers?

Hi Ms Grando! After reading your questions, I did a little bit of research. The developers look at the aftermath of the test. With these results, they can determine whether or not the mass of the car should be increased, decreased, or if more safety features, and conclude with the overall safety of the car. Every car has a “crumple zone”, an area of the car that is designed specifically to absorb the force of impact in collisions so that the force of the impact is not transferred to the passengers. I hope these answers satisfy your questions :)

Awesome blog, I really enjoyed the example of the car crash to Newton’s third law, it really helps give a better understanding of the law in a circumstance most people see in everyday life, but never notice. I also Love your gravitor of Apu from the simpsons. Although I regret to mention I notice one equation on your blog of newtons third law, is there any forces that could relate to this opposite and equal reactions that Newton mentions. Maybe forces like Gravity… and the net force our bodies apply to the ground when we are walking or the Applied forces from the cars before they crash and how the horizontal net force is being affected. And to answer your question on what other aspects in everyday life do you experience Newton’s third law, I notice it in construction in jackhammers, and wrecking balls, where both have to use acceleration and mass to do their jobs right. Enjoyed the blog

i like how you end your topic with a question and how you relate to the video! i think you should add more calculations or use diagrams to show that the reaction and the action forces of both cars are equal

I also like how you chose a common issue inside the world and directed it to the age bracket where worries least about safety. Maybe seeing these videos and reading more about this topic will allow them to drive safer. Interesting how you set up your blog very creative and a good use of emphasis on important words/phrases.

I like your into about newton’s third law. I also liked the fact how you explained the video that you posted and you ended off with a question. I feel you should include more equations and more diagrams that explain about you topic. Overall, it is a great blog.

Hey this was an interesting topic because im a new driver and the last thing i wanna do is crash! One thing that i liked was how you explained the video and made its thought connect to your thoughts. One thing that could be improved is you could add how car materials and design effect the crash and saftey ratings of vehicles.

I liked that your topic was organized and easy to read through. It was simple and understandable, along with a great choice of the video you added. I would suggest that you add some calculations and maybe some more visuals.

Good example of Newton’s third law of motion before getting into the main part of your topic, it helps the reader understand the concept and notice how it happens in our every day lives. You had a good video and information on the physic of car crashes, but you could also include diagrams (maybe before and after) that show the forces acting on cars as they approach each other and collide.

Good job Shiv. I enjoyed reading about your example for Newton’s third law. It was interesting. My only suggestion is that you add some sample calculations for Newton’s laws and I was also wondering which types of cars have the greatest crumple zones?

Great post. You demonstrated the physics behind a car crash with a high degree of understanding. This is a topic that every student our age should be paying attention too because this is the age where we start driving, and we really should know of the dangers of driving before it is too late. I enjoyed the video, and it helped me understand the topic better. I’ve noticed that with new cars, there are a lot of safety features that prevent injuries during accidents. What physics do these new technological advancements in vehicles use that prevents injuries?

This was an interesting blog. Especially for me because I love cars! I thought that this blog was nice but I also thought that you could have benefited by talking more about other forces that apply when a car crashes such as energy, work, and gravity. One question, I have heard that when a car crashes, the energy is absorbed by the car so that the person in the car doesn’t get affected by the energy absorbed, and car makers are getting better and better at letting the car absorb the force. What is the physics behind that, and how does it work?

Great blog Shiv ! You were able to demonstrate newton’s third law in a real life application effectively ! Your video was also able to help with that explanation. Maybe you can add some diagrams of the forces acting between two cars in a crash or some equations. Other than that, good job.